Method and apparatus for increasing effective contrast ratio and brightness yields for digital light valve image projectors

ABSTRACT

The present invention is a method and apparatus for increasing the effective contrast ratio and brightness yields for digital light valve image projectors using a variable luminance control mechanism (VLCM), associated with the projector optics, for modifying the light output and provide a correction thereto; and an adaptive luminance control module (ALCM) for receiving signals from said video input board, said adaptive luminance control module producing a signal on a VLCM bus connecting the variable luminance control mechanism and the adaptive luminance control module, said signal causing the variable luminance control mechanism to change the luminance of the light output and provide a corrected video signal for the projector.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.10/913,744 entitled “METHOD AND APPARATUS FOR INCREASING EFFECTIVECONTRAST RATIO AND BRIGHTNESS YIELDS FOR DIGITAL LIGHT VALVE IMAGEPROJECTORS”, filed with the U.S. Patent and Trademark Office on Aug. 6,2004 by the inventors herein, which application claims priority under 35U.S.C. .sctn. 119(e) from U.S. Provisional Patent Application No.60/493,739, filed Aug. 8, 2003, for a “METHOD AND APPARATUS FORINCREASING EFFECTIVE CONTRAST RATIO AND BRIGHTNESS YIELDS FOR DIGITALLIGHT VALVE IMAGE PROJECTORS,” by E. Allen, and Provisional PatentApplication No. 60/557,620, filed Jun. 27, 2004, for an “IMPROVEDOPTICAL SHUTTER WITH ECLIPSE VOICE COIL MOTOR (EVCM),” by T. Strade etal., all of which are hereby incorporated by reference in their entiretyfor their teachings.

FIELD OF THE INVENTION

This invention relates generally to a method and apparatus forincreasing effective contrast ratio and brightness yields for digitallight valve image projectors, and more particularly to setting thegeneral level of scene illumination removing this control, at leastpartially, from the duty list of the imager(s) and thereby increasingoverall contrast ratio and increasing the available ANSI dynamic for lowbrightness images/scenes.

BACKGROUND AND SUMMARY

Heretofore, a number of patents and publications have disclosed meansfor controlling the intensity, contrast or dynamic range of a projectionimage, the relevant portions of which may be briefly summarized asfollows:

U.S. Pat. No. 5,386,253 to Fielding, issued Jan. 31, 1995, andincorporated herein by reference in its entirety, discusses exemplaryprojection systems utilizing one or more spatial light modulators(SLMs).

U.S. Pat. No. 5,717,422 to Fergason, issued Feb. 10, 1998, discloses adisplay and method employing a passive light modulator, a source oflight, and a control for controlling the intensity of light supplied tothe light modulator to provide images of good contrast for both brightand dark scenes. A method of displaying an image, which uses a passivelight modulating display apparatus, includes controlling the intensityof light illuminating the display apparatus as a function of abrightness characteristic of the image.

US-20040001184A1 by Gibbons et al., published Jan. 21, 2004 (andclaiming priority from PCT/US01/21367 filed Jul. 2, 2001), teaches asystem for addressing deficiencies of electronic, SLM-employingprojectors. It does so using techniques described as being capable ofproviding images of sufficient overall quality that they may be used invenues instead of, or in addition to, traditional large-format filmprojectors without disturbing audience perception that the viewed imagesare of high quality. The publication describes techniques includingpre-modulation, luminance compensation, and partial luminancecompensation.

A data and/or video projector's light valve optical engine is generallya device that uses means of modulating a fixed or variable light sourcebased on either the reflective or transmissive properties of certainimaging panels. These panels may be Liquid Crystal Display (LCD), LiquidCrystal on Silicon (LCOS & SXRD), a Digital Micromirror Device (DMD) orany other pixelized imager panel(s) system.

Most high-lumen output video projectors use an arc lamp for theilluminating source. In the case of LCD and LCOS versions of imagers thewhite light produced by such lamps is usually separated into the primarycolors of red, green, and blue using dichroic color-separating optics.Arc lamp separated colors are then passed through a polarizing filter towork with polarizing beam splitters. The primary color beams are eitherpassed through the LCD panels (a transmissive technology) or reflectedfrom LCOS panels (a reflective technology). However imperfections inboth the means of polarization of the beams and the inability of theimagers to completely block the illumination source results in areduction of the contrast ratio (CR) of the image.

DMD imagers utilize non-polarized light from the illumination source,may or may not contain beam splitters and contain micro-mirrors thatdirect light through the lens or away from the lens as directed to formthe image (another reflective technology). Primarily, diffraction &reflection of light from various planes within the DMD and less thanperfect reflectivity of the mirrors themselves results in a reduction ofthe contrast ratio of the image.

For the purposes of this presentation optical components between theillumination source (lamp) and the outermost exit lens are consideredthe projector's “optical engine.” Optical engines include but are notlimited to dichroic beam splitters (where applicable), polarizers (whereapplicable), imaging panel(s), re-combining optics (where applicable),light tunnels, light collimators, irises, etc.

The present invention is directed to a method and apparatus to increasethe effective contrast ratio and brightness yields for all types ofdata/video digital light valve image projectors. This concept ispartially based on the fact that the contrast ratio dynamic from suchdevices displaying a “bright” image is limited to a projector'ssimultaneous contrast capability (commonly measured as ANSI contrastratio—hereinafter ANSI CR), and the fact that the ON/OFF contrast ratiolimits a projector's “dark” image's dynamic to a point much less than alight-valve projector's ANSI CR capability. It is also based on the factthat current light valve projectors (LCD, LCOS, SXRD, DMD) haveextremely limited ON/OFF contrast ratios, when compared to standardcathode ray tube (CRT) type projectors, and are in need of this designimprovement.

CRT type projectors are able to maintain, for the most part, full ANSICR regardless of the image's general level of illumination due to thevariable intensity output capability of their tubes. However, lightvalve projectors have a steady state of illumination source (i.e. alamp) that is modulated solely by the imaging device(s). As such it isnecessary for the imaging devices, regardless of type (DMD/LCOS//SXRD,LCD, etc) within the projector, to generate all of the image's dynamics.Since all these imaging devices “leak” light to varying degrees (i.e.,areas intended to be dark or off are not completely dark), this limitsthe projector's ability to maintain full ANSI CR, particularly at thelower intensity levels resulting in a lack of depth in the image.

Attempts have been made in the past to vary a projector lamp's output toboost on/off CR, but these have failed to provide significantimprovement due to the limited variable light output range of lamps(maintaining sustained ignition) and the fact that varying the lampintensity drastically changes the color balance (balance in spectraloutput) of the lamp, thus limiting most light-valve projectors to one ortwo illumination levels from their bulbs (current examples: bright andeconomy-lamp modes). None of the lamp intensity schemes interact inconcert with the imager(s) or help to produce better engine contrastratio yield as the invention described herein does, neither doprojectors with simple fixed or manually or electrically adjustableirises. The present invention relies on the technological premise thatdigital imaging devices perform three basic functions, among others, inorder to generate a usable image for display:

-   -   1) modulate imager(s) with a source signal to create a        recognizable pattern (i.e. an image),    -   2) set the general level of scene illumination; and    -   3) “paint” the image to create color(s) with a variety of        available techniques.

The present invention focuses on the second function set forthabove—setting the general level of scene illumination, where thisfunction is removed, at least partially, from the duty list of theimager(s) for the primary purpose of increasing overall contrast ratioand increasing the available ANSI dynamic for low-brightnessimages/scenes. In order to accomplish this function outside of thetypical projection optical imaging engine, one aspect of the inventionis intended for implementation in two stages, which are described inmore detail below.

A first component of the present invention is a variable luminancecontrol mechanism (VLCM). The VLCM is, in one embodiment, a specialhigh-speed, temperature-resistant, electronically controllable irissystem placed before, after or inside the optical engine of anylight-valve projection device. A single (or multiple in some cases) irissystem will be located at the point(s) either pre- and/or post-imager(s)within the optical engine that yields the best balance of results. Thislocation will vary from projector to projector depending upon itsparticular design and on the intended results. In the case of singledigital light processing (DLP) chip optical engines, this calls for asingle iris system placed post-imager at a focal convergence pointlocated post imager. The purpose of this adjustable iris is to vary thegeneral scene illumination level, as the input signal varies, at a speedthat is generally undetectable to the human eye. The main benefit of theluminance control function provided by the iris is extending the ON/OFFcontrast ratio well beyond the ability of the imaging devicesthemselves. In other words, the use of the iris improves the ON/OFFcontrast ratio by lowering the scene illumination on dark scenes to anearly completely off level and thereby reducing the light “leaking”through the optical path of the projector. As will be described below,the use of one, or multiple irises, may also be employed to modulate orcompensate for lamp brightness, including changes in or decay of thelamp/illumination source.

The addition of an iris does not change the color balance of theillumination (lamp) source or the imager(s); it is spectrally neutral inaction. The shape of the iris may also be changed to assist in contrastratio yields. For example, an oval or “cats eye” shaped iris may lenditself to a better contrast ratio yield than round or multi-sided(polygon) versions. Moreover, the present application contemplates thatfuture implementations could also use extremely fast reactingphotosensitive optics that would variably turn darker or lighter toeither enhance or replace the mechanical iris method.

A second component employed in the present invention is an AdaptiveLuminance Control Module (ALCM), which is coupled to the VLCM. The ALCMis a video signal processing system including circuitry and componentsthat will operate and set the variable aperture opening or opacity ofthe VLCM and provide a corrected video signal to the input of theprojector. This electronic luminance processing will follow the videoinput signal, tracking either the general (average) illumination levelor the brightest point(s) in the signal (i.e., peak level detection) orany combination, and will output two different types of signals:

-   -   1) The VLCM drive signal. When fed a resultant, processed        (analog or digital) signal, the VLCM will set the general scene        illumination level. This optimizes both the engine's contrast        (both absolute ON/OFF and ANSI CR) and the lumen output for the        particular level of illumination that is needed to accurately        reproduce the image. The VLCM drive signal is, effectively        proportional to the input intensity of the video image (average        or peak). The present invention contemplates the possibility        that VLCM feedback may be required, and may employ one or more        sensing mechanisms or circuits to indicate VLCM position or        condition.    -   2) The image signal. The video output signal, post processing,        is passed on to the projector's imager stage input. This image        signal is processed and manipulated to take full advantage of        the VLCM optical restriction capability. This unique        relationship is described below. The processing for the image        signal is primarily look-up (gamma) and gain based, along with a        “black level clamp”. Output gamma will not track identically to        the input signal's gamma; in other words, it will “adapt” to the        input signal's illumination dynamics for optimization with the        iris. There are various algorithms that will enable the desired        functionality and will improve the technology. As used herein,        “black level clamp” is a term describing the input to output        signal proportion at 0 IRE. In other words, no matter what        function the gamma tables and algorithms perform on the video        signal; “0” input always equals “0” output.

In accordance with the present invention, there is provided an apparatusfor improving the operation of a digital image projector, comprising: avideo input board of the projector; a optical engine of the projector,said optical engine receiving video signals and generating a lightoutput for at least one primary color from; optics for transforming thelight output from said light engine to a focused image for projection toa display screen; a variable luminance control mechanism (VLCM),associated with the optics, for receiving the light output and provide acorrection thereto; and an adaptive luminance control module (ALCM) orprocessor, for receiving signals from said video input board, saidadaptive luminance control module producing a signal on a VLCM busconnecting the variable luminance control mechanism and the adaptiveluminance control module, said signal causing the variable luminancecontrol mechanism to change the luminance of the light output andprovide a corrected video signal from the projector.

In accordance with another aspect of the present invention, there isprovided a method for improving the operation of a digital imageprojector, comprising the steps of: receiving image signals from a videoinput board in the projector; using an adaptive luminance controlmodule, producing an output signal on a VLCM bus connected to theadaptive luminance control module, said signal providing controlinformation for a variable luminance control mechanism, located withinthe optical path of the projector; and adjusting the variable luminancecontrol mechanism to produce a corrected light output from theprojector.

In accordance with yet another aspect of the present invention, there isprovided an apparatus for improving the operation of a digital imageprojector, comprising: a video input board of the projector; a lightengine of the projector, said light engine receiving video signals andgenerating a light output for at least one primary color there from;optics for transforming the light output from said light engine to afocused image for projection to a display screen; a variable luminancecontrol mechanism, associated with the optics, for receiving the lightoutput and provide a correction thereto; and an adaptive luminancecontrol module, for receiving signals from said video input board, saidadaptive luminance control module producing a control signal, whereinsaid variable luminance control mechanism operates in response to thecontrol signal to change the luminance of the light output and provide acorrected video signal for the projector

In accordance with another aspect of the present invention, there isprovided a method for improving the operation of a digital imageprojector, comprising the steps of: receiving video signals from a videoinput board in the projector; and producing a first signal, using anadaptive luminance control module, to provide control information for avariable luminance control mechanism located within the optical path ofthe projector and a second signal which is a modified video signal,whereby the variable luminance control mechanism operates to produce amodified light output from said digital image projector.

One aspect of the invention is based on the discovery that the generallevel of scene illumination may be adjusted in a video projector toimprove the effective contrast ratio. This discovery avoids problemsthat arise in conventional light projectors due to light leakage, etc.Using aspects of the present invention, overall contrast ratio and theavailable ANSI dynamic for low-brightness images/scenes may besignificantly increased. In order to accomplish this function outside ofthe typical projection-imaging engine, this aspect is implemented usingthe ALCP and VLCM described herein.

The techniques described herein are advantageous because they can beadapted to any of a number of light projectors. As a result of theinvention, it is possible to produce digital light projection systemswith improved overall contrast ratios and available ANSI dynamics forlow brightness images/scenes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are exemplary schematic overviews of a conventional lightprojection system with the components of the present inventionincorporated therein;

FIG. 3 is a schematic block diagram illustrating components of theadaptive luminance control module in accordance with an aspect of thepresent invention.

FIG. 4 is a perspective view of a shutter system in accordance with anaspect of the present invention;

FIGS. 5 and 6 are orthographic representations of the system of FIG. 4in alternative scales;

FIG. 7 is a simple schematic diagram illustrating a possible applicationof the present invention;

FIGS. 8 and 9 are alternative embodiments of the present inventionincluding aspects of the embodiments depicted in FIGS. 1 and 2; and

FIG. 10 is a flow diagram generally illustrating the analysis of a framein accordance with an aspect of the present invention.

The present invention will be described in connection with a preferredembodiment, however, it will be understood that there is no intent tolimit the invention to the embodiment described. On the contrary, theintent is to cover all alternatives, modifications, and equivalents asmay be included within the spirit and scope of the invention as definedby the appended claims.

DETAILED DESCRIPTION

For a general understanding of the present invention, reference is madeto the drawings. In the drawings, like reference numerals have been usedthroughout to designate identical elements.

As depicted in FIG. 1, a conventional light valve projection displaysystem includes a video input board 16, where video signals are receivedand processed to produce a plurality of channels (e.g., 3-colors) ofcolor signals. The color signals are then directed to a light engine 12in which the color signals are used to transform light from a source 14into a light output on each of the three color channels, the lightoutput then being directed through optics represented by lens 10 forprojection onto a screen or display surface 18. As depicted in FIGS. 1and 2, the present invention includes at least two additionalcomponents, a variable luminance control mechanism (VLCM) 13 and anadaptive luminance control module (ALCM) or processor 15.

In one embodiment, the VLCM 13 is a special high-speed, temperatureresistant, electronically controllable iris system placed into theoptical path of any light-valve projection device. A single-iris, or insome cases multiple-iris, system will be located either pre-(FIG. 2) orpost-imager(s) (FIG. 1) within the optical engine, so as to yield thebest balance of results. This location will likely vary from projectorto projector depending upon the particular design of the projector. Inthe case of single digital light processing chip optical engines asingle iris system, placed post-imager at the focal convergence point,would be used. The purpose of the adjustable iris is to vary the generalscene illumination level as the input signal varies—at a speed that isgenerally undetectable to the human eye. The primary result is that theON/OFF contrast ratio is extended well beyond the ability of theconventional imaging devices themselves. For example, by using the iristo lower over-all lower light level for a dark scene the impact ofsmaller changes in luminance for individual regions of the image will beenhanced—thereby improving the contrast ratio. Further details of anexemplary iris system are described below relative to FIGS. 4-7.

The addition of an iris does not change the color balance of theillumination (lamp) source or the imager(s) as it is spectrally neutralin action. As will be appreciated, in a three-chip/iris system (e.g.,FIG. 9), where each color may be separately controlled by an iris, theremay be a change to color balance if the colors are differentlymodulated. As an alternative to a mechanical iris as described relativeto VLCM 13, the present invention further contemplates the use ofextremely fast reacting photosensitive optical components, whereby thecomponents would variably turn darker or lighter to either enhance orreplace the mechanical iris as described above.

For example, the NanoChromics™ display, provided by NTERA Ltd. may beemployed in the control of scene illumination. The NanoChromics™ displayis an electrochromic device forming with a nanoporous-nanocrystallinefilm having a controllable transmittance in response to electricalsignals as described, for example, in U.S. Pat. No. 6,301,038 toFitzmaurice, et al., issued Oct. 9, 2001 for an “ELECTROCHROMIC SYSTEM,”the teachings of which are incorporated herein by reference in theirentirety. Alternatively, a NanoChromics™ display may also be employed asa secondary modulation device, where in addition to a primary ALCM, asecondary modulation device such as the NanoChromics™ display could beused to further control the contrast ratio of a projection system. Forexample, as depicted in FIGS. 8 and 9, the ALCMs 813 or 913, 923,individually or in combination, could be employed to provide a secondarymodulation source.

As depicted in FIG. 1, the adaptive luminance control module orprocessor 15 is coupled to the VLCM via a bus 17 (VLCM bus) or similarmeans for transferring data and control signals. The adaptive luminancecontrol module is a video signal processing system operating on aconventional processor or specialized signal processing chip or chipsetin accordance with pre-programmed instructions. The ALCM will operateand set the variable aperture opening or opacity of the VLCM(s) andprovide a corrected video signal to the input of the projector. In otherwords, in addition to analyzing the video data to determine theappropriate VLCM settings or characteristics for a projected scene, theALCM further operates to modify the image signal to the projectionsystem. The electronic processing of the image signal will follow thevideo input signal to track, for example, the general (average)illumination level or the brightest point(s) in the signal (i.e., peaklevel detection). In alternative embodiments, it is contemplated thatthe processing may include any combination of average or peak leveldetection, and further including luminance detection by percentage. Inany event, the processing will result in the output of at least twotypes of signals, as follows:

-   -   1) a VLCM drive signal; and    -   2) a processed image signal.

For the VLCM drive signal, when fed a resultant, processed (analog ordigital) signal, the VLCM will set the general scene illumination level.This optimizes both the engine's contrast (both ON/OFF and it'srelationship to ANSI CR) and the lumen output for the particular levelof illumination that is needed to accurately reproduce the image. TheVLCM drive signal is, effectively proportional to the input intensity ofthe video image (average or peak or any combination). Furthermore, Thepresent invention further contemplates the possibility that VLCMfeedback may be required, and may employ one or more sensors or similarsensing mechanisms or circuits to indicate a VLCM characteristic such asposition or condition.

Also, as noted above, the video output signal, post processing, ispassed on to the projector's input. This image signal will be processedand manipulated to take full advantage of the VLCM optical restrictioncapability. This unique relationship is described in detail below. Theprocessing for the image signal is primarily gamma look up and gainbased, along with a “black level clamp”. Output gamma will not trackidentically to the input signal's gamma; in other words, it will “adapt”to the input signal's illumination dynamics for optimization with theiris or modulator of the VLCM. There are various algorithms that willenable the desired functionality and will improve the technology, thegeneral nature of which are described generally below and with respectto FIG. 10. As used herein, “black level clamp” is a term describing theinput to output signal proportion at zero IRE. In other words, no matterwhat function the gamma tables and algorithms perform on the videosignal; “0” input always equals “0” output.

Output gamma will not track identically to the input signal's gamma. Inother words, it will “adapt” to the input signal's illumination dynamicsfor optimization with the iris. As will be appreciated by those skilledin the art, there are various algorithms that may be employed to furtherimprove the response of the system.

Referring briefly to FIG. 10, depicted therein is a general flow diagramillustrating an exemplary series of processing steps that may beemployed to produce the signals or outputs described above. Asrepresented in the figure, the following notation is used: P_(y)represents pixel luminance; P_(w) is the weighted pixel value; P_(p) isthe peak pixel value; and APL an average pixel level.

More specifically, for a given frame of video, P_(RGB) represents apixel in RGB space, which is stored in the frame. Subsequently, thecalculation would proceed to determine the Average Picture Level (APL).In one embodiment, the APL is a sum of the luminance across all pixels,which is then divided by the pixel count. As illustrated in FIG. 10, theWeighted Average Pixel Level (APL_(W)) is based on the sum of squares orother multiplier (weighting) scheme as carried out at block 1020, andthen divided by pixel count to determine an average at block 1040. Asindicated by the LUT (Look-Up Table) in block 1020, a preferredembodiment would include the ability to modify the table or valuestherein so that any algorithm for weighting could be applied. For thecalculation of the peak value as represented by block 1030, the peak mayemploy a peak luminance, a peak independent component value (e.g., Red,Green, Blue), or even a range of component values (Pr, Pb).

The present invention further contemplates the use of other approachesto analyze a frame or scene, including a histogram, where for eachpossible value of a pixel, the numbers of pixels of that value arecounted. Alternatively, motion, cross-correlation or other algorithmsmay be employed to determine if a frame/scene change has occurred. Asanother alternative, the spatial distribution/object size may beanalyzed, for example: (i) using regional histogram or APL analysis;(ii) using adjacent pixels or blocks; (iii) using size or measure thesize of an object in pixels horizontally/vertically; and/or (iv) bytaking a contrast image and size inside the contours. Subsequently,using one or more of the results from above analyses the results may beemployed to do one or more of the following:

-   -   Select a LUT based on APL alone to act as a correction to the        stored pixel data;    -   Use the peak values to limit which of the LUT's may be selected;    -   Match the histogram to a set of window/threshold curves and use        the index of the matched curve to determine the LUT and image        correction;    -   Based on the LUT selection pick an IRIS position; or    -   Alternatively select an iris position based on any of the above        calculations and select the LUT from the iris position.

Furthermore, the following MatLab code represents another alternativemethod for analyzing and correcting gamma, where three primaryoperations are carried out:

-   -   function void=gammacorrection(cr,lightoutput,adjust,suffix);    -   %where cr is the contrast ratio of the system at the stated        lightout. adjust is a boolean to decide whether to do the        eclipse process.    -   %Please note that most of this design script was written back        when a continuously variable iris was the preferred means.    -   %A stepper motor will require a little more work but this        analysis still holds.

%A stepper motor implementation is slightly more complex and beingunique isn't addressed here. %##############Step 1: Gammadesign####################### %This step is the system design part. Thisportion is performed before hand. gamma = 2.35 %This is a compromisegamma for the incoming video. Incoming video is   encoded between 2.2and 2.5. This should work well enough maximageintensity = 2756; %giventhe algorithm below in step 2 this is the maximum   value for a 1280 ×720 white image. %thresholds for image brightness based on the equationshown in step two. These values   are pretty much imperically derived.high = 351 %image brightness needed for iris to be fully open. Any imagebrighter than   this will be displayed at full light. low 10 %imagebrightness needed for iris to be fully closed. Darker images than thiswill   not close the iris further.  %Note: Ihe values I have here arethrough my own testing. high should be no less than   351 which iseither a 75 IRE blue or 75 IRE red image  %I expect for a 3:1 contractratio I expect about 40% of movie images to be higher than   the highregion, about 20% to be darker than the lower region and 40% to be  imbetween %Designing the amount of light contraction in the image.minlight = 1/3 %amount of light at the smallest iris opening as a ratioof full light. In   other words we are doing a 3:1 contraction. minstep= .99 %ideally this is the maximum decrease in lightlevel you couldperform at   each iris position based on Poynton's work. numofluts =ceil(log10(minlight)/log10(minstep)) %number of look up tables  required to satisfy minstep. lightlevelsindex = 0:numofluts;  %simpleindex array 0,1,2, up to numofluts. lightlevels = minstep.{circumflexover ( )}lightlevelsindex;  %lightlevels corresponding to the LUTs:  1.0, .99, .9801, . . . , 333 lightlevels = fliplr(lightlevels) %Thisputs the lightlevels from darkest to brightest  %Note: the abovevariables assume that we have complete control of the iris. Obviously  a stepper motor will have discreet position that might not be .9801 oforiginal light. %The principal of operation is to darken the lightsource (i.e. close the iris) and digitally   brighten the image tocompensate % Obviously something has to be compromised and in this caseit is the infrequently used   upper IRE's on dark images which need tobe elegantly “crushed”. unalteredratio = 2.1; %for incoming video, inrelation to the missinglevel, this is the   portion of the incomingimage that we want to preserve unaltered. unalteredlightlevels=10.{circumflex over ( )}(log10(lightleveIs).*unalteredratio) %at eachof the light   levels this the unaltered %for 50% lightoutput we want topreserve everything from .23 light level down so %.23/.5 = .46 of themirror dutycycle %.46{circumflex over ( )}(1/2.35) = .7186 of the signalinput signal needs to be uncompressed after   compensation % RGBratio =0:1/255:1;  %8bit RGB in terms of percent of full signal RGBintensity =RGBratio.{circumflex over ( )}gamma %De-gamma is applied. Now the RGBvalues are   in a percent of light output. luts = zeros(numofluts +1,256); for i = 1:numofluts   dark = RGBintensity <=unalteredlightlevels(i);   bright = RGBintensity >=unalteredlightlevels(i);   lowintensities = (RGBintensity.*dark)/lightlevels(i); %this expands the RGB    levels[intensity,location] = max(lowintensities);    %this finds what RGBvalue    that compression has to start at   gammacompression =log10(intensity)/log10(RGBratio(location));   highintensities =(RGBratio .*bright).{circumflex over ( )}gammacompression; %thiscompresses   newRGBintensities = lowintensities + highintensities;  %combining the bright    portion of the table with the dark newRGBratio = newRGBintensities.{circumflex over ( )}(1/gamma);  %Nowwe are back in   gamma encoded world  luts(i,:) round(newRGBratio*255);end luts(numofluts + 1,:) = 0:255; %a bright image is unaltered so 0 to255 in equals 0 to 255   out. luts(40,:) luts(numofluts + 1,:) lutindex= zeros(1 ,maximageintensity + 1);    %As stated below the max image  intensity calculation is 2756 lutindex(1:low + 1) = 1;    %from thelow threshold down the brightest lut is chosen   and the darkest irisposition Iutindex(high + 1:maximageintensity +1 ) = numofluts + 1; %fromthe high threshold up   the lut is unchanged and the lightest irisposition is used lutindexstep = numofluts/(high-low) lutindex(low +1:high + 1) = round(lutindexstep*(0:high-low)) + 1 %adding in the middle  ground lightindex = lightlevels(lutindex) %Using the lutindex valueswe can determine the   corresponding lightindex %compensate for lessthan perfect black %CRatmin = 5000 %CRatmax = 2000 %CRdifference =CRatmin-CRatmax; %CRstepsize = CRdifference/length(lightlevelsindex);%CRsteps = CRatmax:CRstepsize:CRatmin; %Blacklevels = 1/CRsteps;%minimum percent change %###############Step 2: Applyingmap###################### %In an actual projector design this step wouldneed to be performed continuously on each   frame coming in. Here it isperformed on stills for dummy = 1:100    %for all the test images thatyou want to do control c will take    you out at any point. %LOADingimage file if (˜exist(‘fid’))    [filename,pathname] =uigetfile(strcat(‘C:\ . . . \*.bmp’),‘Load Data’);    fname =strcat(pathname,filename);   imin = imread(fname,‘bmp’); %reading inimage in three seperate 8 bit arrays-one    for R,G, andB elseif (lid <=0)    error(‘Invalid File ID’); end %The intensity equation =G{circumflex over ( )}2*2 + B{circumflex over ( )}2 + R{circumflex over( )}2 on the upper three bits while the image is still    in 24 bitcolor. imdouble = double(imin); %changing from unit8 format to doublefloats which Matlab    uses imnormalized = imdouble/255; figure(1)%plotting picture image(imnormalized); if adjust     %adjust for theprojector would always be on intensity = bitshift(imdouble,−5,8);%bitshifting to only use the top three bits; size(intensity)min(min(min(intensity))) max(max(max(intensity))) intensity(1,1,1)intensity = intensity.{circumflex over ( )}2; %squaring every element inimdouble. intensity(1,1,1) intensity(:,:,2) =bitshift(intensity(:,:,2),1,32); %doubling the intensity of green pixels   since they are brighter intensity(2,1,1) intensity =sum(sum(sum(intensity))) %summing up entire image intensity to get value   of brightness of the incoming image. %Intensity can range anywherefrom 0 for black up to 180633600 for a full white image   (7{circumflexover ( )}7*(1 + 2 + 1)*1280*720) intensitysmall =bitshift(intensity,−16,12) %this brings the number down to 0 to 2756  and thus the lutindex equals 2757 values. lutneeded =lutindex(intensitysmall + 1) %lutindex is an index file which points to  which of the roughly 100 or so available LUT's to use lut =luts(lutneeded,:) %getting the necessary 256 value lut output =lut(imdouble + 1); %mapping the old RGB values to new RGB valueslightneeded = lightindex(intensitysmall + 1) %this specifies what lightlevel the iris   should be as a ratio of full white. %Ultimatelylightneeded would need to be the step number on the stepper motor to get  the light correct. %Also at this moment lightneeded is linked 1:1 tolutneeded figure(2) outputnormalized = output/255;image(outputnormalized) end %######Step 3: Simulating/Demonstrating thebefore and after effect##### %The actual image manipulation stops atstep 2. This step is mearly for   simulating/demonstrating what aneclipse DLP projector would look like %by using a computer CRT whichtypically has CR's in the 10000:1 or more range. crindex =cr./Iightlevels%This states that the contrast ratio goes up by an equalfactor   of the amount of light reduced (approximately true) CRTcr =10000; CRTblacklevel = 1/CRTcr; if ˜adjust    %if the no Eclipse gammaadjustment is wanted to show before   images  outputintensity =imnormalized.{circumflex over ( )}gamma;  outputintensity(1,1,1) blacklevel = 1/cr  outputintensity = (outputintensity + blacklevel)./(1 + blacklevel);  outputintensity(1,1,1)  outputintensity =outputintensity * lightoutput;  outputintensity(1,1,1)  outputintensity= outputintensity - CRTblacklevel;    %compensating for the   computersCRT less than perfect black  outputintensity(1,1,1)  outputintensity =(outputintensity >= 0).*outputintensity; %this caps the blacklevel   noless than 0  outputintensity(1,1,1)  outputnormalized =outputintensity.{circumflex over ( )}(1/gamma);  outputnormalized(1,1,1)else     %if eclipse is wanted to show after images  outputintensity =outputnormalized.{circumflex over ( )}gamma;  outputintensity(1,1,1) lutneeded  cradjusted = crindex(lutneeded)  blacklevel = 1/cradjusted outputintensity = (outputintensity + blacklevel)./(1 + blacklevel); outputintensity(1,1,1)  outputintensity = outputintensity*lightneeded; outputintensity(1,1,1)  outputintensity = outputintensity -CRTblacklevel;   %compensating for the   computers CRT less than perfectblack  outputintensity(1,1,1)  outputintensity = (outputintensity >=0).*outputintensity; %this caps the blacklevel   no less than 0 outputintensity(1,1,1)  outputnormalized = outputintensity.{circumflexover ( )}(1/gamma);  outputnormalized(1,1,1) end figure(3)image(outputnormalized)  filename2 = input(‘press enter to store file(control-c cancels)’,‘s’); %iflength(filename) = =1 & filename(1) ˜= ‘n’ fname = strcat(pathname,filename(1:(length(filename)-4)),suffix,‘.jpg’); %imwrite(outputnormelized,fname,‘bmp’); imwrite(outputnormalized,fname,‘jpg’,‘Quality’,100);  %end end %Thisend closes the step 2 and 3 loop for processing multiple images

Turning next to FIG. 3, depicted therein is a schematic block diagramillustrating components of the adaptive luminance control module (ALCM)15 in accordance with an aspect of the present invention. The ALCMreceives electronic video signals as raw video in any one of a pluralityof formats (based upon the projector) and processes the video signalsinto separate and distinct signals that are suitable for electronicallydriving both an electronic imaging system, such as a typical videoand/or data projector's imaging device(s)/driver(s), and the VLCM 13 viabus 17 (e.g., FIG. 2). The resulting signal sent to the electronicimaging system is ultimately combined optically with the output of thelight engine and VLCM combination to faithfully reproduce the originalelectronic video signal.

In one embodiment, the ALCM consists of five sub-modules: The videoreceiver (VR) 60, the adaptive gamma processor (AGP) 64, the luminancelevel processor (LLP) 62, the video transmitter (VT) 68, and the VLCMcontroller (VLC) 66. The video receiver 60 sub-module portion of theALCM performs the task of assuring input signal compatibility andconversion from various sources. The video receiver buffers themultiple-format electronic video input signals in a memory (not shown)and inputs them to a subsequent sub-module, the luminance levelprocessor 62. The electronic video signals, input to the video receiveras raw video signals, may consist of, but are not limited to, compositevideo, S-video, component video, RGB video, RGBHV video, DVI video, HDMIvideo, etc.

The luminance level processor (LLP), sub-module 62, receives a videosignal from the receiver 60 and passes an unaltered video signal to theAGP sub-module 64. It also derives, from this video pass-through signal,a selectable averaged, or peak, signal(s) and sends this information tothe AGP in the form of a luminance content signal. It will beappreciated that various signal-sampling methodologies may be employedto sample and determine luminance levels of the video signals, and thatany individual or combination of luminance content level detectiontechniques may be employed by the present invention. For example, aweighted average may be employed where brighter pixels receive greaterweighting. The luminance level processor also inputs to the VLCMcontroller 66, a luminance control signal that is proportional to theluminance content signal sent to the AGP. The luminance content signalinput to the AGP represents a percentage equal to or greater than 100%and the luminance control signal to the VLC represents a percentageequal to or less than 100%. In other words, the signals are based abouta normative, 100% level. As the LLP 62 instructs the VLCM to restrictthe optical throughput it also instructs the AGP 64 to utilize a look-up(gamma) table to increase the video signal the light output of theoptical engine by a proportional amount. In this example the actualoptical restriction amount and the video signal luminance increase areinverse and proportional.

After receiving the electronic video signal from the LLP sub-module 62,the adaptive gamma processor (AGP) sub-module performs the task ofre-mapping the input voltage-to-output levels based on a set of definedlookup tables 65. The table to be used for a particular video frame isdetermined by the luminance content signal from the LLP and theresulting video output signal from the AGP is sent to the videotransmitter sub-module 68. In other words, the luminance content signalacts as the table selector or table index, and the individual videosignals then select the location or point into the table and the AGPoutputs the signal stored in the table at the position pointed to. Itwill be appreciated by those skilled in the art of signal processing,that the lookup tables employed may be preprogrammed and stored inmemory associated with AGP 64. Moreover, it may be possible to load orselect from one or more sets of lookup tables, based upon auser-selected preference or environmental variables such as roomlighting. As will be further appreciated, the lookup tables effectivelyperform a transformation operation, by remapping the signals, and thatalternative methods of performing such transformations are intended tobe included within the scope of the present invention, including but notlimited to gate arrays and similar programmable devices.

Similarly, since existing illumination sources utilize lamps/bulbs whoselight output typically decreases with age, the present invention mayalso be employed to compensate for the output/brightness decay. Thelook-up tables can be further modified to allow a built-in illuminationsource (lamp/bulb) lamp output level decay algorithm to be coupled withan indicator of lamp life (e.g., an hour meter, counter, timer, etc.) toprovide predicted steady-state illumination over the life of the bulbutilizing the VCLM as the illumination compensation modulator. Another,more accurate, method would utilize a lamp/bulb output sensor to measurethe actual output so as to characterize any decay, and thereby enablethe ACLM to implement real-time correction information instead ofpredicted decay values. In any of the alternatives, the ACLM would, inresponse to an indication of the decay characteristic, adjust the VCLMto compensate for the decay or change in illumination. In other words,referring to FIGS. 2 and 9, for example, a light sensor or life timer(not shown) would provide feedback to the ALCM, which in turn wouldadjust the VLCM 13 or 913 to open or allow more illumination therethrough, to compensate for brightness decay.

In addition to and in concert with this brightness decay compensatingfunction, the ACLM can be programmed to limit or control brightness sothat the system provides almost any specific brightness or maximumillumination level from the projector. For example: a specific projectorinstallation requires a 900 lumen projector due to screen size, screenfabric gain and ambient illumination. A 1500 lumen projector may beutilized and programmed to output maximum of 900 lumens. Due to thepresent invention's VCLM control capabilities, there are no losses ofon/off or ANSI contrast ratios with this function. Furthermore, in thisexample the ALCM and VLCM modules have as much as 600 available lumens(the unused balance) as an available range to perform the brightnessdecay compensation.

In one embodiment, the AGP lookup tables are based on mathematicalformulas with two fixed constants and a variable scale: 100% (average orpeak) input signal usually outputs as 100% (average or peak) and a 0%input signal is output at 0%. In-between the 0% and 100% levels arevalues determined by entries in the lookup (or gamma) tables. Thesetables are derived from values optimized for contrast ratio yield andconsider the specific projector optical engine employed. These lookuptables are graduated on percentages, scales or steps that ultimatelycorrespond to I.R.E. signal levels.

The video transmitter (VT) sub-module 68 receives the processed videosignal information from the AGP and buffers the signal, for transmissioncompatibility, into the imager driver system of the particular opticalor light engine(s) employed.

The variable luminance controller (VLC), sub-module 66, receives thebuffered luminance control signal from the LLP 62 and operates (drives)the VLCM directly via the VLCM Control bus 17 (FIG. 1). The VLC providescurrent, voltage and buffering drive signal to the VLCM that is inproportion to the luminance control signal from the LLP. The VLC may beequipped with a positional feedback sensor and associated circuitry forcalibration when a mechanical VLCM is employed, or a thermal,transmissive or similar sensor and feedback circuit when anelectronically controllable photo-resistive VLCM is employed.

In another embodiment, the present invention further contemplatespre-encoding the data for both the ALCM/VLCM settings and adjustments.For instance, the media on which a movie or similar performance isprovided may include pre-encoded data that characterizes desiredillumination settings, adjustments, etc. and control circuitry such asthe ALCM could sense and receive such data from the media, either as apre-defined lookup table or as “hints” that are encoded. Although thepresent invention is intended to operate in real-time, it will beappreciated that the limitations of certain hardware and controlcircuitry may impose a delay in operation and that in the event of suchdelay, related processing of data must be similarly delayed so as toremain in synchronization. For example, if a medium includedillumination data or hints, the system utilizing such information mayneed to employ techniques to “look-ahead,” and collect such informationso as to avoid delaying output that relies or utilizes the information.

Referring next FIGS. 4-6, depicted therein is an exemplary iris-typeVLCM. The multi-iris shutter system 100 is driven by a voice coil motor110. Shutter system 100 is based on magneto-static principals; so as toprovide a very efficient flux path (not shown) around an existing frame120 containing lightweight titanium iris leaves 130 and 132. The inertiaforces generated by the displaced coil-leaf systems (130, 132 and coil136) are preferably balanced in order to reduce the vibrations. The endresult is an extremely fast and efficient method to modulate the lightlevels by rapidly varying the size of an aperture 140 created usingmultiple irises leaves 130 and 132. Alternative devices to actuate theshutter system include servo and/or stepper motors configured in a wayto move the opposing iris leaves back and forth to open and close theaperture. It should be understood that the magnetic circuit could alsobe totally to one side of the assembly if space permits.

Coil 136 is a wound tubular magnet wire, where the impedance of the coilis dependant on the number and size of the turns—for example a terminalresistance of approximately 12 ohms. The coil is supported by a “Wishbone” structure 150 that provides added rigidity to the leaf and thecoil structure. The slide mechanism introduced in the frame 120 providesa minimum friction while guiding the 0.45 inch movement of the irisleaves based on the size of the opening 140. The total dead mass of thecoil 136 is counter balanced by the iris and “wish bone” components.Magnets 160 and 162 are pre-magnetized and assembled into the returnpath depicted generally by reference numeral 168, using an alignmentfixture. The polarity of magnets 160 and 162 is such that they alternatefrom “North” to “South” as the flux travels through the circuit andgenerates a non-uniform 5,000 gauss field in the air gap denoted byreference numeral 168. The geometry of the pole structure provides aunique distribution of flux as seen by the VCM coil 136. This isnecessary since the velocity profile requires very fast acceleration anddecelerations during an 18 msec. cycle. This is part of anelectromechanical device that drives the flux from the source “magnet”through the double air gap 168 and back. A low carbon steel alloy can beused since the magnetic saturation allows the flux density to operatearound 18,000 gauss without running the risk of saturating the circuit.

Leaves 130 and 132 are two ultra thin leaves, each of approximately 0.5mm in thickness, that can travel a total of approximately 12 mm (0.45inch) from the center point relative to one another, hence forming anaperture or shutter system with a final shape similar to that of a “CatsEye” although other shapes can be utilized to effect, differently, theamount of light allowed through for the various positions of the leaves.Although any leaf thickness can be used it will be optimized to providethe best mass for the acceleration necessary to obtain the designedperformance. The innovative leaf/blade design allows high intensitylight exposure without any distortion or degradation in performance. Forincreased durability, it will be appreciated that a titanium alloy maybe used to form the leaf shapes. Although titanium is employed for itslow-weight and high strength and temperature stability, the presentinvention further contemplates alternative metals, alloys and similarmaterials. It will be further appreciated that the leaves or othercomponents of the iris assembly may be temperature resistant so as toprovide consistent operation over a range of temperatures, for examplefrom about 25° C. to at least about 250° C. The frame 120 providesprecise location for the iris, and the leaves slide within 0.58 mm widegrooves 170 in the frame 120. The entire inner surfaces of the groovesrequire anti-friction treatment to reduce the sliding friction of theleaves. In assembly of the frame within the VCM, it will be appreciatedthat an alignment tool may be employed to position the frame withrespect to the VCM coil.

The alignment tool could be used in conjunction with the assembly tocenter the iris opening on the light path through the system.Alternatively if an offset opening improves the capabilities of thesystem then that offset position could also be obtained through use ofan alignment tool.

Referring next to FIG. 7, there is depicted a general schematicillustration of one embodiment of the present invention. In essence theEVCM receives an electronic signal from a digital amplifier 100, or moreparticularly the VLCM controller 66 described above, that causes theiris leaf to move. The movement is tracked by a digital linear encoder,quadrature encoder, optical linear encoder, or similar sensor, such asan optical infrared sensor, (e.g., in a computer optical mouse). TheEVCM can be controlled with precision that permits incremental movementsor absolute positioning. The optical sensor 420 will most likely be aconsumer product-based design similar to a computer optical mousetracking system. Flat flexible cable, or a printed circuit traces, wouldallow for maximum movements of the iris leaves, and faster terminationby combining encoder signals, encoder power, two VCM phase current, andground connections. The control signals from the signal processor 400will be amplified to power the actuator of shutter system 100 and todrive the coil 136 forward and backward. Although described as a signalprocessor, the required functionality may be accomplished using anysuitable control components, including an operational amplifier ormicroprocessor for position feedback and such components would be partof the ALCM described above.

In summary, the VCM receives an electronic signal from a digitalamplifier that causes the iris leaf to move. The movement is tracked bya sensor such that the EVCM can be controlled with precision thatpermits 50 nm incremental moves in less than 18 ms. With respect to theabove description then, it is to be realized that the optimumdimensional relationships for the parts of the iris-type VLCM, toinclude variations in size, materials, shape, form, function and mannerof operation, assembly and use, are deemed readily apparent and obviousto one skilled in the art, and all equivalent relationships to thoseillustrated in the drawings and described in the specification areintended to be encompassed by the present invention.

Having described the various components and general operation of anembodiment of the present invention, attention is now directed to anexample of the operation of the ALCM 15. Consider a video (frame) signalof 20% average luminance input into the video receiver 60, where it isbuffered and sent to the luminance level processor 62, and where eachframe is averaged and/or peak detected to determine what processingshould be implemented to the signal. The luminance level processor 62decides the best way to process this particular video frame is by afactor of two; thus, a luminance content signal is derived and sent tothe AGP and a proportional luminance control signal is derived and sentto the VLC 66.

The luminance content signal directs the AGP 64 to use a particularlookup table. The AGP, using the lookup table, re-maps the video signalfrom the VR to 40% average luminance by direction of the selectedexample table and passes the resulting video signal to the videotransmitter 68 where it is buffered into the projector'simager(s)/driver(s) which renders an average output level of 40% (i.e.light output capacity of the optical engine). The LLP's inverse andproportional luminance control signal of 50% is sent to the VLC 66, thenbuffered and sent to the VLCM 36.

The VLCM, via optical or other means, restricts the projector's opticalengine maximum light output capability by 50% and therefore restores theprojector's brightness output to the original signal level's intended20% average. In this example the contrast ratio yield from the opticalengine and VLCM combination under the control of the ALCM (at a 20%video signal) is approximately twice that which would be available froman otherwise identical but unequipped optical engine.

To further illustrate the operation of the present invention, thefollowing examples are provided for purposes of illustration, and arenot intended to limit the scope of the present invention.

To better understand the yields of this invention, consider a projectorusing the single chip DLP projector such as a Virtuoso HT720T. Thefollowing is assumed for both examples presented below: out-of-the-boxthe HT720 projector exhibits close to 1000 lumens and a 1200-1 ON/OFFcontrast ratio (@ 6500) and an ANSI contrast of about 300 to 350-1.

First an alternative embodiment is described, with the VLCM and simpleradaptive processing in the form of automatic tracking of the generalillumination levels (average illumination) and the black level clamp:

-   -   a. Assumption: set VLCM limits range for maximum closure that        yields 400-lumens and for a maximum opening that yields 1000        lumens (i.e. no aperture restriction).    -   b. Assumption: the VLCM full open yields a contrast ratio of        1200-1 and in full closure yields 2500-1. This is an accurate        number based on several experiment versions and the fact that        the projector, when provided with a certain fixed in-between        value iris, produces 600 lumens and a contrast ratio of 2000-1.        This is the result of the optical engine's contrast ratio        increasing substantially as the aperture restricts, but at the        cost of less light output.    -   c. In this example, with the VLCM partially closed, the        projector yields 2500-1 contrast ratio @ 400 lumens. However,        the projector will still be capable of generating an image @        1000 lumens with the VLCM fully open. The formula for the        resulting usable contrast ratio is 2500×2.5=6250-1 contrast        ratio. The 2.5× multiplier is derived from the available image        brightness increasing from 400 to 1000 lumens: a 2.5-fold        increase.

As a general rule the real limit for projector contrast ratio withbrighter images is represented by the ANSI contrast ratio. What thisdesign accomplishes is that it extends available ANSI CR to much lowergeneral illumination levels. Simply put, ANSI CR is severely limited byON/OFF contrast ratio at low IRE signals.

For example, a 5 IRE signal is actually less than 1% of an imagingdevice's full luminance output capability. If a typical projectorexhibits a contrast ratio of 1200-1, then for a 5 IRE peak scene, themaximum contrast ratio actually available for use in the resulting imageis approximately 12-1 (the difference between on/off CR and a 1% peakscene). In the simple example outlined above, the contrast ratio at 5IRE is improved significantly to approximately 62-1. Since the human eyeis sensitive to these very low levels of contrast ratio (anything below200/300-1 is generally deemed detrimental) the image loses both depthand dynamic. Since both numbers are still below the ANSI capability ofthe projector it is demonstrable that further improvement may beprovided by this invention.

In yet another example, an adaptive iris and peak based adaptiveprocessing in the form of automatic tracking of the brightest object(peak illumination detection) in an image and the “black level clamp” isemployed:

-   -   a. Assumption: the VLCM range is set for maximum closure that        yields near 100 lumens and for a maximum opening that yields        1000 lumens (again no restriction).    -   b. Assumption: the VLCM, full open, yields contrast ratio of        1200-1 and in full closure around 3500-1 (3500-1 contrast ratio        is achievable when a 1000 lumen projector is limited to only 100        lumen maximum output). Again, this is a realistic number based        on multiple experiments/observations.    -   c. In this second example, with VLCM closed, the projector        yields 3500-1 contrast ratio @ around 100 lumens. However, the        projector will still be capable of generating an image @ 1000        lumens with the VLCM set at no restriction (full open). Again,        the formula for the resultant usable is contrast ratio=3500×“X”.        And again, the “X” multiplier is derived from the image        brightness increasing from lower lumen yield level to 1000        lumens. If, the resulting optimum iris closure lumen yield is        100 lumens, then the available contrast ratio is        3500×10=35,000-1

In this second example, the contrast ratio at 5 IRE is improved to 350-1which is now a level that matches/exceeds the unit's ANSI CR capability.In reality it is possible, at best, to equal but never exceed aprojector's ANSI CR capability at very low illumination levels. Thisexample yields results similar to what CRT units can generate at thisillumination level resulting in a similar depth and dynamics in theimage.

Dynamic processing in the ALCM compensates for various VLCM modulatedbrightness levels. It is important to understand the role of the dynamicprocessing in how it relates to the function of the iris. If the secondexample above is considered, a 5 IRE peak signal is somewhere within theimage, and it would, without gamma re-processing, really be much lowerin intensity on the screen due to the VLCM being constricted by a signalfrom the processor. However the adaptive processing will, in addition tosetting the VLCM aperture at about 90% restriction, reinterpret the 5IRE and output a much higher video signal for the projector; near 100IRE. This in turn instructs the projector's imager to operate near or at100% intensity (see ALCM operation example above) and, in turn,overcomes the optical brightness restriction imposed by the VLCM and thepeak portion of the image appears as the proper 5 IRE level on thescreen. It is this concept; to take a low-brightness signal(peak/average) and apply it as a high-brightness signal (peak/average)to the imager(s) and restrict it back to proper level with the VLCM,which yields the greatest improvement.

One might consider this in the following manner: currently light-valveprojectors can output lumens right up to their maximum output abilityregardless of what is really needed to reproduce the brightest peak inan image or frame. Unless the image calls for a 100 IRE component in theframe, this “excess” light output capacity reduces available contrastratio due to imperfections in the optical engine. The ALCM/VLVM equippedoptical engine in effect produces only enough light to reproduce theaverage or peak illumination called for in a particular frame or imageand no more. Calculating the multiple input to output gamma curves iscritical for this system's operation. Mapping and measuring the correctcurves is required, and the minimum number of VLCM “stops” required tooperate seamlessly require investigation into each type of opticalengine to determine the optimum operation. It is further anticipatedthat there may be some practical limitations of the present invention.For example, few low-level scenes are “somewhat uniform” inillumination. A bright streetlight or car headlight or a flashlight ator near 100 IRE, present in an otherwise very dark scene, would “only”yield a contrast ratio that is native to the projector. However, such“peak” image items are usually presented at something less than 100 IREand this adaptive system will make the most out of them by boostingthese bright items to 100% imager output capacity and by inverselyrestricting the VLCM the proper amount. In other words, it is possibleto artificially decrease the luminance for these bright items because itdecreases the instantaneous black level and this can improve the overallimage fidelity compared to keeping the higher black level. It ispossible with processing to artificially expand, to a degree, theillumination changes between gamma “steps” particularly at lower levels.This can result in increased “depth” perception for low IRE scenes fromthe projector and better handling of these steps by the projector'simager(s). This will be applicable to any light-valve projector equippedwith this technology.

Another advantage with this technology is the reduction of DLP “dither.”“Dither” is the result of a time-division scheme to allow DLP equippedprojectors the ability to display very-low IRE signals that are beyondthe minimum on/off state and time-per-frame capability of the DMDchip(s) micro-mirror's. With the present invention it is no longernecessary, in lower illumination scenes, to drive the DMD to those IRElevels that produce the worst dither states. In other words a 0.1 IREsignal might place the DMD into dither (or time/division) to try andcreate that low level signal. With this technology an approximately 0.1IRE signal would be reprocessed as something much higher, up to 1 IREand be restricted by the iris back to a 0.1 IRE yield on the screen thusreducing the amount of “dithering” in very low illumination scenes.Although generally color separation artifact (commonly called rainbows)neutral when applied to DMD panel optical engines, aspects of thepresent invention may aid in the reduction of rainbows (time/divisioncolor separation artifacts), particularly at lower IRE illuminationlevels. Another benefit of the invention is the ability of a projectormanufacturer to reprioritize the design goals of a projector's opticalengine. Almost universally, contrast ratio is sacrificed for brightnessas a compromise in optical engine design. With this invention, theconsideration of design requirements may be modified to allow brightnessand other aspects of image reproduction to be higher in priority and inturn use this invention's capability to boost the contrast ratio withoutsacrificing brightness.

In recapitulation, the present invention is a method and apparatus forincreasing effective contrast ratio and brightness yields for digitallight valve image projectors using a variable luminance controlmechanism (VLCM), associated with the projector optics, for receivingthe light output and provide a correction thereto; and an adaptiveluminance control module (ALCM) for receiving signals from said videoinput board, said adaptive luminance control module producing a signalon, a VLCM bus connecting the variable luminance control mechanism andthe adaptive luminance control module, said signal causing the variableluminance control mechanism to change the luminance of the light outputand provide a corrected video signal for the projector. It is,therefore, apparent that there has been provided, in accordance with thepresent invention, a method and apparatus for increasing effectivecontrast ratio and brightness yields for digital light valve imageprojectors. While this invention has been described in conjunction withpreferred embodiments thereof, it is evident that many alternatives,modifications, and variations will be apparent to those skilled in theart. Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims.

The claims, as originally presented and as they may be amended,encompass variations, alternatives, modifications, improvements,equivalents, and substantial equivalents of the embodiments andteachings disclosed herein, including those that are presentlyunforeseen or unappreciated, and that, for example, may arise fromapplicants/patentees and others.

What is claimed is:
 1. An apparatus for improving the operation of adigital image projector, comprising: a video input board of theprojector; a light engine of the projector, said light engine receivingvideo signals and generating a light output for at least one primarycolor there from; optics for transforming the light output from saidlight engine to a focused image for projection to a display screen; avariable luminance control mechanism, associated with the optics, forreceiving the light output and provide a correction thereto; and anadaptive luminance control module, for receiving signals from said videoinput board, said adaptive luminance control module producing a controlsignal, wherein said variable luminance control mechanism operates inresponse to the control signal to change the luminance of the lightoutput and provide a corrected video signal for the projector.
 2. Theapparatus of claim 1, wherein the adaptive luminance control modulecomprises: a video receiver for receiving video signals and bufferingthe signals; a luminance level processor for deriving a characteristicof the buffered video signals and producing a luminance content signal;and an adaptive gamma processor, receiving the luminance content signalfrom the luminance level processor, for looking-up a modified videosignal in response to the buffered video signal and the luminancecontent signal.
 3. The apparatus of claim 2, wherein the adaptiveluminance control module further comprises a variable luminancecontroller for receiving the luminance content signal and producing, inresponse, a control signal including a current, voltage and bufferingdrive signal to the variable luminance control mechanism that is inproportion to the luminance content signal.
 4. The apparatus of claim 1,wherein the variable luminance control mechanism comprises anelectronically controllable iris system.
 5. The apparatus of claim 4,wherein the electronically controllable iris system is temperatureresistant so as to provide consistent operation over a range oftemperatures.
 6. The apparatus of claim 4, wherein the electronicallycontrollable iris system is a single iris located at a focal convergencepoint to vary the general scene illumination level.
 7. The apparatus ofclaim 4, wherein the variable luminance control mechanism furthercomprises a sensor to produce a signal indicating a characteristic ofthe variable luminance control mechanism.
 8. The apparatus of claim 7,wherein the characteristic of the variable luminance control mechanismis a representation of the size of an opening of a variable iris.
 9. Theapparatus of claim 3, wherein the variable luminance controller producesan illumination control signal to control a level of illuminationprovided by a light source.
 10. The apparatus of claim 4, wherein theelectronically controllable iris system is responsive to the controlsignal and operates to alter the position of at least one componenttherein.
 11. The apparatus of claim 1, wherein the variable luminancecontrol mechanism comprises: a primary iris system operating in responseto the control signal to change the luminance of the light output; and asecondary luminance modulation mechanism that also operates in responseto the control signal to change the luminance of the light output. 12.The apparatus of claim 11, wherein the secondary luminance modulationmechanism is an iris system.
 13. The apparatus of claim 11, wherein thesecondary luminance modulation mechanism is an electrochromic device.13. The apparatus of claim 13, wherein the electrochromic device is adisplay including a nanocrystalline film.
 14. A method for improving theoperation of a digital image projector, comprising the steps of:receiving video signals from a video input board in the projector; andproducing a first signal, using an adaptive luminance control module, toprovide control information for a variable luminance control mechanismlocated within the optical path of the projector and a second signalwhich is a modified video signal, whereby the variable luminance controlmechanism operates to produce a modified light output from said digitalimage projector.
 15. The method of claim 14, further comprising thesteps of: receiving video signals and buffering the signals; deriving acharacteristic of the buffered video signals and producing a luminancecontent signal; and receiving the luminance content signal andlooking-up a modified video signal in response to the buffered videosignal and the luminance content signal.
 16. The method of claim 15,further comprising the step of receiving the luminance content signaland producing, in response thereto, a control signal including acurrent, voltage and buffering drive signal in proportion to theluminance content signal.
 17. The method of claim 14, wherein thevariable luminance control mechanism includes an electronicallycontrollable iris and wherein the method further comprises the step ofaltering the position of at least one component in the iris in responseto the control signal.
 18. The method of claim 14, wherein the variableluminance control mechanism includes an electrochromic device andwherein the method further comprises the step of altering thetransmittance of at least a portion of the electrochromic device inresponse to the control signal.